Police had arrested the pair on Thursday morning after the girl was found dead in an apartment in Karlskrona. The man (31) and woman (30) are not the girl's parents, who were overseas at the time.
"We have worked with the investigation in order to obtain sufficient material for the prosecutor to make a remand request and to be permitted to detain the individuals," Lotta Hansson, press spokesperson of the Blekinge police, told the Expressen newspaper.
The girl, referred to as Yara by Swedish media, had been residing in Sweden since February 2013. Her parents were in Gaza when they heard the news their daughter was dead on Facebook.
"It's come as a total shock. It is terrible," the girl's father was quoted as telling Expressen.
He added; "We can't believe that this is true, we do not know what to believe. Now we need to wait for the investigation in Sweden in order to find out what happened."
The girl's death has stunned Karlskrona, with floral tributes left outside her school and where she lived. It has since emerged that social services were alerted to the girl's situation with her guardians over a year ago.
When the couple suspected of murder were arrested, police pointed out they were not the girl's parents but had a "certain relationship" with her. It is understood that the 31-year old man is related to the victim and the arrested pair were, in fact, her guardians in Sweden.
Since the arrests police have declined to reveal details about the nature of the crime.
Prosecutor Pernilla Åström said that the arrested pair were being remanded on probable cause as they could potentially destroy evidence or impede the investigation. She added there was also the possibility they could continue carrying out criminal activities.
The pair will be formally remanded in Kristianstad on Saturday afternoon, with negotiations on the details of their arrest to take place on Sunday at the police station.